Torque converters couple the engine to the transmission and operate to transfer engine torque to the transmission, which in turn transfers torque to the wheels. More specifically, the torque converter, which includes a clutch, operates to increase torque while reducing engine speed. Torque converters provide well-known advantages due to the infinitely variable conversion of speed and torque. Operation, or application, of the torque converter clutch is typically controlled by a solenoid.
The California Air Resources Board On-Board Diagnostics, more commonly known simply as OBD-II, is a set of regulations which prescribe certain standards relating to vehicular emissions. Currently, these regulations require that if the torque converter clutch is inadvertently applied as a result of a purely electronic component failure, then the MIL must be illuminated.
Existing strategies for testing the torque converter clutch control system only perform electrical "presence" tests. However, according to the OBD-II requirements, a purely electrical "presence" test of the torque converter clutch control system is not sufficient to eliminate the electronics as a contributor.
It would be desirable, therefore, to devise a torque converter clutch functional test which distinguishes between OBD-II electronic component (e.g. solenoids) failures and other, non-OBD-II subsystem failures (e.g. mechanical, hydraulic, and the like). Although a failed torque converter clutch solenoid (an electronic component failure) and a stuck bypass clutch control valve (a mechanical failure) could both cause the torque converter to lockup when a lockup has not been requested by the powertrain control module, only the former requires illumination of the MIL under the regulations.